1. Field of the Invention
This invention relates to electrical connectors. More particularly it relates to an improved subsea electrical connector designed to operate under sustained conditions of high voltage and high amperage.
2. Description of the Prior Art
With the recent rapid growth in development of natural resources in the offshore areas of the world it has become necessary to adapt and develop machinery and equipment for operation under water. An example of such an adaptation has been the development of subsea systems used for the production of oil and gas from offshore reservoirs. These systems are designed to handle a variety of tasks on the sea floor at water depths extending to several thousand feet. Such tasks may include well completions, oil and gas separation, pumping operations, flowline connections, and various maintenance tasks requiring diver or manipulator assistance. To provide the electrical power necessary to remotely operate the subsea systems, reliable electrical cables and connectors, operable at high voltages and currents, are required. Other examples of subsea machinery having high electrical power requirements are underwater construction and mining equipment, subsea work vehicles, and power transmission lines.
Most electrical connectors developed for underwater use must first be engaged above water before they can be submerged. Such connectors, known as "dry" connectors, are impractical where it is necessary to frequently mate and separate the connector. To do so requires bringing the connector to the surface each time a mating or disengagement is required. This procedure is especially impractical at great depths where a long length of cable must be brought to the surface in order to retrieve the connector.
Subsea connectors which may be safely connected or disengaged under water are referred to as "wet" electrical connectors. Typically, wet connectors have contacts that are sealed or protected from exposure to moisture or sea water. U.S. Pat. Nos. 3,491,326 (F. Pfister et al.) and 3,508,188 (J. R. Buck) disclose examples of disengageable connectors having protected contacts. Specifically, Pfister discloses a spring biased, hollow cylinder within the female receptacle half of a connector which shields the female contacts from the external environment when the connector is disengaged. When mated the male pin depresses the cylinder sufficiently so that the male contacts engage the female contacts. Seal rings positioned in front of the female contact serve to wipe any water or debris off the male pin as it enters the female receptacle. Buck et al. similarly discloses a slidable, piston-like sealing member biased by a spring which serves to protect the female contact until depressed by the male pin.
Wet connectors must also be capable of operating at depths where there exists a significant hydrostatic pressure exerted by the surrounding sea water. Sealing mechanisms such as those discussed above are capable of withstanding a limited hydrostatic pressure. Obviously, as the connector is subjected to greater differential pressures it becomes increasingly difficult to provide an effective sealing means having a sealing capacity in excess of the pressure differential. A pressure balanced connector such as that disclosed in U.S. Pat. No. 3,845,450 (J. C. Cole et al.) employs the use of a dielectric fluid which is present within both halves of the connector. A deformable plastic cable surrounding the dielectric fluid serves to pressurize the fluid to ambient pressure thereby eliminating any differential pressure across the fluid tight seals within the connector.
A design employing both a piston actuated sealing means and a dielectric oil pressure compensator is disclosed in U.S. Pat. No. 3,729,699 (E. M. Briggs et al.) and in OTC Paper 1976, "Development of an Underwater Mateable High-Power Cable Connector" by J. F. McCartney and J. V. Wilson (1974). The connector of Briggs et al. incorporates a dummy piston to seal the female electrical contact which is displaced by the male pin. A piston-cylinder hydraulic means is also used to pressure balance the internal pressure of the dielectric fluid with the external sea water pressure.
Although the design of wet electrical connectors, as described above, represents a considerable advance over dry connectors, the wet connectors developed to data have been limited in their power capacity. Presently, wet connectors have a maximum AC voltage limitation of about 4000 to 5000 volts AC RMS and a maximum amperage of about 100 amps. For all practical purposes, however, under conditions of continued submergence, high pressure and repeated matings, the connectors presently available have a sustained voltage limitation of about 1500 to 3000 volts AC RMS at 50 amps. Such power limitations for underwater connectors in turn limit the electrical power which can be made available to subsea equipment and machinery. There is, therefore, a need in the art for an underwater electrical connector capable of reliably operating at great depths while carrying a very high voltage with high current capacity.